The present invention relates to a liquid crystal display device, and more particularly to the liquid crystal display device and a method for fabricating thereof, in which a light shielding layer and an insulating layer are formed by anodizing a portion of a metal layer to prevent damage to a gate insulating layer caused by the light shielding layer.
An active matrix liquid crystal display (AM LCD) has a thin film transistor(TFT) in each pixel. By operation of this TFT, the LCD is driven. The AM LCD is a transparent type LCD in which light generated from a back light mounted on its rear part passes through the pixel region. Since the picture is provided only in the area that the pixel electrode is formed, the light passing through regions of the TFT, gate bus lines, and data bus lines deteriorates the degree of the distinction in the AM LCD. Thus, it is needed to prevent the leakage of the light through the regions of the TFT, the gate bus line, and the data bus line.
FIG. 1 is a plan view showing one pixel of conventional LCD. In this figure, the gate bus line 1 and the data bus line 2 extend in the horizontal and vertical directions and define the pixel region. The pixel electrode 9 is formed in the pixel region and the TFT is formed at the intersection of the gate bus line 1 and the data bus line in the pixel region. A gate electrode 3 and source/drain electrodes 4 of the TFT are electrically connected to the gate bus line 1 and the pixel electrode 9, respectively. In the regions of the TFT, the gate bus line 1, and the data bus line 2, a light shielding layer 7 is formed to prevent the leakage of the light therethrough.
The light shielding layer 7 is formed on the TFT array substrate or the color filter layer substrate. In the LCD with the light shielding layer 7 formed on the color filter layer substrate, the incorrect attachment of the substrates causes the deterioration of the aperture ratio.
In the LCD with the light shielding layer 7 formed on the TFT array substrate, as shown in FIG. 2, the formation of the TFT, the gate bus line 1, and the data bus line 2 directly on the light shielding layer 7 improves the aperture ratio. That is, the light shielding layer 7, which is a metal layer such as Cr layer and CrOx layer, is formed by the sputtering and photoetching process on a substrate 10 and an insulating layer 15 including SiOx and SiNx is formed by plasma chemical vapor deposition (plasma CVD) process thereon. The gate electrode 3 is formed on the insulating layer 15 and a gate insulating layer 16 is formed thereon. A semiconductor layer 5 and the source/drain electrodes 4 are sequentially formed on the gate insulating layer 16. A passivation layer 18, having a contact hole, is formed over the semiconductor layer 5 and the gate insulating layer 16, so that the source/drain electrodes 4 are electrically connected to the pixel electrode 9.
In the LCD shown in FIG. 2, since the light shielding layer 7 is correctly formed under the TFT, the gate bus line 1, and the data bus line 2, it does not cover the pixel region. Therefore, the aperture ratio is improved. However, since the gate insulating layer 16 is damaged by the step caused by the light shielding layer 7, the pixel electrode and the gate electrode are short-circuited.